It blinds; it burns; it looks kind of pretty. An invasive, poisonous plant known as giant hogweed, or Heracleum mantegazzianum, is attacking western Ontario.

The plant is a member of the carrot or parsley family, and as described in a brochure (pdf) from the Michigan Department of Agriculture, 20th century gardeners cultivated the giant for its impressive size and for its stem’s purple coloring. But it soon broke out of gardens and arboretums, its seeds finding soil outside of captivity.

Besides Canada, the plant has also appeared in the northern United States (both east and west) and as far south as Maryland. Ontario officials are concerned with the plants’ continuing spread–it was most recently sighted in Renfrew County–and have urged anyone who spots it to contact them immediately.

Giant Hogweed can grow to almost twenty feet tall and five feet wide, and each plant can produce tens of thousands of seeds. Sap on your skin can give you ugly blisters, the CBC reports, and sap in your eyes could cause blindness.

Jeff Muzzi, manager of forestry services for Renfrew County, told the CBC that, despite its heft, the weed is a stealthy attacker.

“[Exposure] could be inadvertent,” Muzzi said. “You might not even know it’s here, [just] walk into it and happen to break a leaf. The next thing you know, you’ve got these nasty burns.”

Renfrew County officials are attempting to thwart the toxic plant’s leafy grip by distributing pamphlet warnings and, as the CBC reports, through “weed-whacking campaigns.”

Some guy beat me to it. Return of the Giant Hogweed is an eerie song that goes right along with this invasive eerie plant.

Brian Too

What’s with all the awful plants these days? Giant Hogweed, that underwater seaweed in the Mediterranean that nothing can eat, rock snot (seriously!) in the rivers.

The worst thing you had to deal with when I was a kid was Poison Ivy.

http://www.thepoisongarden.co.uk John Robertson

Weed-whacking is not the way to tackle giant hogweed. I’ve spoken to many people who had weed-whacked an area of ground without realising that there were young giant hogweed plants present. They all ended up with numerous small burns where drops of juice from the plant had landed on the skin.

Then, last year, I experienced it for myself. Out walking along a riverbank, a friend used his walking pole to knock a plant down and I felt one drop of juice hit me on the face just above the lip. A day later I had a small red mark which was tender to the touch. And, this is the thing about giant hogweed, this year the mark comes back if I go out in the sun without using a high factor block. If that’s what one drop did imagine how bad it can get.

Incidentally, I think there’s an extra nought in the number of seeds. Most sources say 50,000 which is still plenty. The seeds are quite large and heavy and tend to just drop close to the plant but, because it often grows on riverbanks, they can get spread in the winter if there is flooding to wash them downstream.

Though I’ve never read of anyone dying as a result of exposure to giant hogweed, I think it’s a nastier plant than all the other potentially fatal poisonous plants simply because it has no benefits or uses.

http://ranggaw0636.student.ipb.ac.id/ ranggaw0636

It’s scary to see what a small plant could do to you

Joseph Calamia

John, Thanks for the comment and for telling us about your experience with Giant Hogweed.

I found the 500,000 seed count in the CBC story, linked above. After reading your comment, I went back and looked at several other sources; most say the number of seeds is in the tens of thousands range–with a max around 100,000.

I’ve made a change in the post above to reflect this. Sorry about the mistake, and thanks for letting us know. Also, I wanted to say that I enjoyed looking through your website on poisonous plants linked through your comment.

Lauren

I saw a huge bunch of these while out walking in Waterloo with my mom a week ago; we thought they were huge flowers. Today after reading this, I called the city and reported it, though they said they’ve already killed 150 weeds already. Apparently Kitchener refuses to do anything about it.

http://www.thepoisongarden.co.uk John Robertson

Joseph Calamia

Thanks. Really 50,000 or 500,000 is still a huge amount.

Lauren’s comment is interesting. I’ve been reading a number of reports from Canada where some local administrations are looking to deal with every single plant. Over here, in Scotland, giant hogweed seems to be the most common plant in Edinburgh and the city council’s position is that they will give advise to landowners if they ask for it.

fraser

I just found out I have Hogweed on my property, we have kids we have told them about it, but unsure who is responsible. Is it the duty of the county we live in or will our plea’s be ignored and how best to get rid of it.